Simple Retry Mechanism

 

The simplest way to retry an asynchronous operation in Spring Boot is to use a for loop to try the operation a certain number of times. Here’s an example:

 

@Service
public class MyService {
    @Async
    public CompletableFuture<String> doSomethingAsync() {
        // time-consuming operation
        return CompletableFuture.completedFuture("Done");
    }
}

 

@RestController
public class MyController {
    @Autowired
    private MyService myService;

    @GetMapping("/retry")
    public CompletableFuture<String> handleRetryRequest() throws InterruptedException {
        int retries = 3;
        for (int i = 0; i < retries; i++) {
            try {
                CompletableFuture<String> future = myService.doSomethingAsync();
                String result = future.get();
                return CompletableFuture.completedFuture(result);
            } catch (Exception e) {
                // retry the operation
                Thread.sleep(1000);
            }
        }
        return CompletableFuture.completedFuture("Failed after " + retries + " retries");
    }
}

 

In this example, we define a method called handleRetryRequest() that tries to execute the doSomethingAsync() method of MyService up to three times. If the operation fails, we sleep for one second before trying again. If the operation still fails after three attempts, we return a CompletableFuture object with the message “Failed after 3 retries”.

Retry with Exponential Backoff

 

A more advanced way to retry an asynchronous operation in Spring Boot is to use exponential backoff. Exponential backoff is a technique that involves increasing the wait time between retries exponentially, to reduce the likelihood of overloading the system. Here’s an example:

 

@Service
public class MyService {
    @Async
    @Retryable(maxAttempts = 5, backoff = @Backoff(delay = 100, multiplier = 2))
    public CompletableFuture<String> doSomethingAsync() {
        // time-consuming operation
        return CompletableFuture.completedFuture("Done");
    }

    @Recover
    public CompletableFuture<String> recoverFromException(Exception e) {
        return CompletableFuture.completedFuture("Failed after 5 retries");
    }
}

 

@RestController
public class MyController {
    @Autowired
    private MyService myService;

    @GetMapping("/retry")
    public CompletableFuture<String> handleRetryRequest() {
        CompletableFuture<String> future = myService.doSomethingAsync();
        return future;
    }
}

 

In this example, we use the @Retryable annotation to specify that the doSomethingAsync() method should be retried up to five times, with an initial delay of 100 milliseconds and a multiplier of 2. This means that the delay between retries will increase exponentially (i.e., 100 milliseconds, 200 milliseconds, 400 milliseconds, etc.). If the operation still fails after five attempts, the recoverFromException() method will be called, which returns a CompletableFuture object with the message “Failed after 5 retries”.

Retry with Circuit Breaker

 

Another advanced way to retry an asynchronous operation in Spring Boot is to use a circuit breaker. A circuit breaker is a design pattern that can prevent a system from overloading or failing when a service is down or slow. Here’s an example:

 

@Service
public class MyService {
    @Async
    @CircuitBreaker(maxAttempts = 3, delay = 1000, resetTimeout = 5000)
    public CompletableFuture<String> doSomethingAsync() {
        // time-consuming operation
        return CompletableFuture.completedFuture("Done");
    }

    @Recover
    public CompletableFuture<String> recoverFromException(CircuitBreakerOpenException e) {       
        return CompletableFuture.completedFuture("Failed after 3 retries (circuit breaker)");
    }
}

 

@Configuration
@EnableCircuitBreaker
public class CircuitBreakerConfig {
    @Bean
    public CircuitBreakerFactory circuitBreakerFactory() {
        return new Resilience4JCircuitBreakerFactory();
    }
}

 

In this example, we use the @CircuitBreaker annotation to specify that the doSomethingAsync() method should be retried up to three times, with a delay of one second between retries, and a reset timeout of five seconds. This means that if the operation fails three times within a five-second period, the circuit breaker will open, and any subsequent attempts to execute the operation will fail immediately. If the operation is successful, the circuit breaker will reset, and the retries will start again.

We also define a recoverFromException() method that returns a CompletableFuture object with the message “Failed after 3 retries (circuit breaker)” if the circuit breaker is open.

Finally, we use the Resilience4j library to implement the circuit breaker pattern. We define a CircuitBreakerFactory bean in a configuration class and annotate it with @EnableCircuitBreaker to enable the circuit breaker in our Spring Boot application.

Overall, these are just a few examples of how you can use Spring Async and retry mechanisms in Spring Boot applications. The specific implementation will depend on your use case and requirements.